The field of the invention relates generally to rotary fan blades and more specifically to a control system for use in adjusting a relative position of a rotary fan blade.
A helicopter is a rotary-wing aircraft that uses a system of power-driven rotor blades to generate lift and thrust that enables the helicopter to climb/descend and to move in a horizontal direction. A pitch of each blade may be individually adjustable to vary the angle of attack and an amount of lift generated by each blade. In some known helicopters, a pilot is provided with a collective pitch control, which changes the pitch on all of the blades simultaneously and equally, and a cyclic pitch control, which constantly varies the pitch of the individual blades through each cycle of rotation. Moreover, varying the pitch of the rotating blades with the cyclic pitch control facilitates control of the pitch and roll.
During forward flight, an asymmetry in lift exists between the advancing-side rotor blades and the retreating-side rotor blades. However, this asymmetry induces a rolling moment to the helicopter when such rotors are rigidly connected. In some other known helicopters, flap hinges or a gimbaled mechanism are used at the root of the rotor blades to substantially eliminate the rolling moment experienced during flight. Additionally, the asymmetry in lift causes the blades to flap which substantially equalizes the lift on the advancing and retreating sides. However, blade flapping also limits the rotor's efficiency in forward flight, and may induce unwanted vibration into the rotor assembly.
In known helicopter rotor blade systems, a rotating blade creates a circular path that is commonly referred to in the art as a rotor plane. Under normal operating conditions, each blade may travel in a sinusoidal path within the rotor plane and be offset with respect to the other blades. However, such rotor blade paths may induce vibrations similar to those induced by an imbalance to the rotor blade system. To facilitate controlling vibration, at least some known helicopters use rotor adjustments as pitch and vibration dampers. Other known helicopters use mechanical feedback systems to sense and counter vibration. Known feedback systems use a mass as a stable reference, and a linkage extending from the mass operates a flap to adjust the rotor blade's angle of attack to counter the vibration. However, locating the origin of the vibration may be difficult. Some known countering systems use a stroboscopic flash lamp to observe painted markings or colored reflectors on the underside of the rotor blades. Adjustments to the rotor pitch may then be made to the identified rotor blades to facilitate controlling vibration.